This invention relates to the use of plant extracts as antioxidants and natural food preservatives, and in particular relates to extracts from the bearberry plant and processes for producing such extracts.
Lipid oxidation in food leads to flavor deterioration, formation of possible toxic products, discoloration of pigments, and loss of nutritional value arising from the destruction of fat-soluble vitamins and essential fatty acids (Nakatani, 1997). The lipids of cooked meats are particularly susceptible to oxidative degradation (e.g. autoxidation). These reactions are generally catalyzed by factors such as singlet oxygen, UV light, heat, meat ions and pigments. Furthermore, the rate at which autoxidation occurs, appears to depend on the degree of lipid unsaturation.
Antioxidants are substances that when present in foods or in the body at low concentrations compared with that of an oxidizable substrate markedly delay or prevent the oxidation of that substrate. Their addition to food prior to thermal processing acts to preserve the quality of the product by retarding autoxidation and rancidity development, as well as discoloration and loss of nutrients. The inhibitory effect of antioxidants has been attributed to preventing first-chain initiation by the donation of a hydrogen atom or an electron, binding metal ion catalysts, decomposing primary oxidation products to non-radical compounds, chain-breaking to prevent continued hydrogen abstraction from substrates, as well as the possible formation of a complex between the antioxidant and the lipid molecule (Dziezak, 1986). The most commonly used food-grade synthetic antioxidants are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tert-butylhydroquinone (TBHQ).
There has been a growing desire to replace traditional synthetic antioxidants in food systems with ones from natural sources due to the suspected carcinogenicity of BHA and BHT (Namiki, 1990; Chen et al., 1992). In particular, research efforts have been focused on the development and utilization of antioxidants from edible plant species. Examples of spices and herbs that have been examined for their antioxidant efficacy in foods include rosemary, sage, oregano, thyme, clove, ginger and marjoram (Wong et al., 1995). In most cases, the active compounds identified in the spices and herbs, or extracts therefrom, have been phenolic acids, flavonoids and/or tannins. One problem with some antioxidant preparations extracted from edible plants is that they may impart a flavor to the food to which they are applied. In some instances, this is a desirable attribute, but more often than not, it isn""t. Kalsec""s DURALOX ((trademark)) and Guardian""s ROSEMARY EXTRACT ((trademark)) are commercially-available food preservatives (in powder and liquid form) containing plant-derived antioxidants.
Synthetic and natural source antioxidants are used to help preserve the quality of a variety of foods. Antioxidants are typically added to foods when they can be easily mixed in with the product. For example in meat products, sodium nitrite is a key additive for curing because it acts as a potent antioxidant. It is either added directly to meat batters during blending or is introduced by injection as a brine pickle into whole muscle products. Natural antioxidants found in spices and herbs are also added to a variety of meat formulations such as uncured sausages (either fresh or cooked) and salamis during blending or into hams by injection as a pickle.
Some traditional synthetic antioxidants, such as BHT, and many natural source antioxidants are not suitable for use in foods that are thermal processed. This is because the antioxidants are heat labile, in that their antioxidative efficacy is degraded or completely destroyed by normal cooking temperatures.
What is needed is a natural source antioxidant that does not impart a flavor to the food to which it is mixed, and which is not heat labile.
According to one aspect, the invention consists of a process for producing a plant extract for use as an antioxidant, particularly as a food preservative, comprising the steps of:
extracting an intermediate extract from plant tissue obtained from the bearberry plant (Arctostaphylos uva-ursi) with a solvent containing ethanol;
loading the intermediate extract on a chromatographic column; and
eluting chlorophyll from the column with a mobile phase comprising hexane.
The step of extracting the intermediate extract may comprise the steps of:
grinding the plant tissue;
mixing the ground plant tissue with the solvent to form a slurry;
filtering the slurry and collecting the supernatant; and
evaporating the ethanol from the supernatant.
The steps of extracting the intermediate extract may also comprise the steps of:
heating the slurry; and
shaking the slurry.
The column may comprise silicic acid.
The process for producing the plant extract may also comprise the step of eluting an ethanol fraction from the column with a mobile phase comprising ethanol.
The process for producing the plant extract may also comprise the step of evaporating the ethanol from the ethanol fraction. The step of evaporating the ethanol from the ethanol fraction may comprise the step of heating the ethanol fraction. The step of evaporating the ethanol from the ethanol fraction may comprise the step of subjecting the ethanol fraction to a pressure which is less than the ambient atmospheric pressure. The step of evaporating the ethanol from the ethanol fraction may comprise the steps of concurrently subjecting the ethanol fraction to a pressure which is less than the ambient atmospheric pressure and heating the ethanol fraction.
According to another aspect, the invention consists of a food preservative comprising an extract from the bearberry plant.
According to another aspect, the invention consists of a food containing a preservative, the preservative comprising an extract from the bearberry plant. The food may comprise a muscle food. The food may comprise pork.